Hong Kong -LRB- CNN -RRB- -- The fragile relationship between China and Japan came under fresh strain Tuesday as ships from both sides crowded into the waters around a disputed group of islands and nearly 170 Japanese lawmakers visited a controversial war memorial .

The Japanese Coast Guard said eight Chinese government ships had entered waters near the contested islands in the East China Sea on Tuesday morning , the largest number to do so at any one time since tensions surrounding the territorial dispute escalated last year . China said its ships were there to monitor the movements of Japanese vessels in the area after a Japanese nationalist group chartered a flotilla of fishing boats to take dozens of activists there .

The Japanese foreign ministry responded by summoning the Chinese ambassador in Tokyo to lodge a strong protest about the Chinese ships ' presence near the uninhabited islands that lie between Okinawa and Taiwan and are known as Senkaku in Japanese and Diaoyu in Chinese . The Chinese ambassador , Cheng Yonghua , retorted that it was the Japanese vessels that were intruding in Chinese territory .

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A day earlier , Beijing had protested to Tokyo about a visit at the weekend by three Japanese cabinet ministers to the Yasukuni Shrine in Tokyo , which honors Japanese people killed while fighting for their country , including convicted war criminals .

Countries that suffered heavily at the hands of the Japanese military before and during World War II , such as China and South Korea , consider the shrine as an emblem of that aggressive period in Japanese history .

But China 's representations failed to deter 168 Japanese members of parliament from visiting the shrine on Tuesday to pay their respects to the war dead , the most to do so in recent years .

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New men in charge

New leaders have taken office in both countries in the past few months : Prime Minister Shinzo Abe in Japan and President Xi Jinping in China . They inherited a highly delicate situation concerning the disputed islands that analysts have warned could spiral out of control -- a concern for the United States , which has a mutual security treaty with Japan .

`` Despite expressions by both governments that they wish to avoid a war , potential for escalation has increased and there is deepening pessimism on both sides over the prospects of a peaceful settlement , '' the International Crisis Group said in a report this month on the tensions between Japan and China .

`` Tokyo and Beijing urgently need to work toward establishing communication mechanisms and strengthening crisis mitigation in order to avoid a larger conflict , '' the report said .

In an indication of the strong stances both sides are taking on the matter , Abe said Tuesday in parliament that any attempt to land on the islands by China would be repelled `` by force . ''

Games of cat and mouse

The relationship between the two nations deteriorated severely in September , when the Japanese government bought several of the islands from a private owner , angering Chinese authorities and provoking a spate of sometimes violent anti-Japanese demonstrations in many Chinese cities .

Since then , the situation has calmed somewhat , but Chinese government ships have continued to frequently sail near the islands , engaging in maritime games of cat and mouse with Japanese Coast Guard vessels . Chinese planes have also flown through the area , prompting Japan to scramble fighter jets .

Both countries claim sovereignty over the remote , rocky islands , which are near important shipping lanes , rich fishing grounds and possible mineral deposits .

Japan currently administers the area , but since September , China has mounted a concerted campaign to try to change the situation .

It says its ships that enter the waters around the islands are conducting routine patrols of Chinese territory . But Japan says they are intruding in its territorial waters .

In the repeated standoffs that result , both sides broadcast warnings to each other 's vessels , ordering them to leave the area that they both claim .

Nationalists ' publicity stunt

The Japanese nationalist group known as Ganbare Nippon this week sent 10 fishing boats carrying dozens of its members to the area around the islands .

A representative for the group , Yasushi Watanabe , said the voyage -- the third by Ganbare Nippon this year -- was aimed at publicizing Japan 's territorial claim to the area , not at landing on the islands .

China 's State Oceanic Administration -LRB- SOA -RRB- said Tuesday that three marine surveillance ships on `` regular patrol duty '' in the area noticed several Japanese ships near the islands , according to the state-run news agency Xinhua .

The SOA said that it dispatched five more ships to join its three vessels near the islands . Together , the eight Chinese ships `` monitored the Japanese ships from different angles , '' it said .

The Japanese Coast Guard said that its vessels had told the Chinese surveillance ships to leave the area , but that they had responded by saying that they were patrolling Chinese territory .

Ganbare Nippon later said its ships had all left the area around the islands .

The weight of history

The competing claims to the islands are intertwined with the region 's complex history .

`` Due to the brutal Japanese occupation of China in the 1930s , sentiments over the status of the Diaoyu/Senkaku Islands run deeper in the Chinese psyche than any other territorial dispute in modern Chinese history , with the exception of Taiwan , '' the International Crisis Group said in its report this month .

China says its sovereignty over the area extends back hundreds of years . Japan says it saw no trace of Chinese control of the islands in an 1885 survey , so formally recognized them as Japanese sovereign territory in 1895 . Japan then sold the islands in 1932 to descendants of the original settlers . The Japanese surrender at the end of World War II in 1945 only served to cloud the issue further .

The islands were administered by the U.S. occupation force after the war . But in 1972 , Washington returned them to Japan as part of its withdrawal from Okinawa .

INTERACTIVE : Asia 's disputed islands -- who claims what ?

CNN 's Jethro Mullen reported and wrote from Hong Kong , and Yoko Wakatsuki reported from Iwaki , Japan . CNN 's Aliza Kassim in Atlanta contributed to this report .

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NEW : A group of boats carrying Japanese nationalists has since left the area

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The number of Chinese ships near the disputed islands is the largest yet , Japan says

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The `` potential for escalation has increased , '' a recent analysis says

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Nearly 170 Japanese lawmakers visit a controversial war memorial